Mesocosm Evaluation of the Species-Selective Potential of Fluridone

• Published in: Journal of aquatic plant management 1997-07, Vol.35, p.41-50
• Main Authors: Netherland, MD, Getsinger, K D, Skogerboe, J D
• Format: Article
• Language: English
• Subjects: Freshwater; Myriophyllum spicatum
• ISSN: 0146-6623

Fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone} was evaluated at rates of 0, 5, 10, and 20 mu g/L in 6,700-L outdoor mesocosm tanks for selective control of the exotic species Eurasian watermilfoil (Myriophyllum spicatum L). Non-target species included elodea (Elodea canadensis Michaux), American pondweed (Potamogeton nodosus Poiret), sago pondweed (Potamogeton pectinatus L), and vallisneria (Vallisneria americana Michaux). Throughout the study, untreated mesocosms were dominated by Eurasian watermilfoil and elodea with limited growth of vallisneria and the two pondweed species. Fluridone treatments were conducted on April 23 and May 23 1995 to determine if plant growth stage affected species selectivity. Fluridone residues were monitored in water and target concentrations were achieved with a measured fluridone half-life of 33 days. The 5 mu g/L treatments in April (90 days of exposure) and May (60 days of exposure) reduced biomass of Eurasian watermilfoil by > 90% in late July, while biomass of non-target species generally exceeded the levels of untreated reference plants. Treatments of 10 and 20 mu g/L also reduced Eurasian watermilfoil biomass by > 90%; however, these application rates also reduced growth several non-target species by > 90%. Chara (Chara spp.) and southern naiad (Najas guadalupensis (Sprengel) Magnus) propagules sprouted and attained high levels of biomass in mesocosms treated at 10 and 20 mu g/L. With the notable exception of vallisneria, plants exposed to 10 and 20 mu g/L in April (90 day exposure) did not show potential for recovery when placed in untreated water for 40 days. In contrast, when transferred to untreated water all species (with the exception of sago pondweed) exposed to 5, 10, and 20 mu g/L in May (60 day exposure) recovered significantly in comparison to plants that remained exposed to low concentrations of fluridone (1 to 4 mu g/L). Results suggest that fluridone can selectively control Eurasian watermilfoil; however, initial treatment rate, length of exposure, and initial biomass of the plants are key factors. The range of fluridone concentrations that provide selective control of Eurasian watermilfoil in a mixed plant community may be quite narrow.